This invention relates to a valve assembly mechanism for a power steering device.
As used herein center line shall, where applicable, be construed as being an axis.
The valve assembly in the power steering device of rack and pinion type shown in FIGS. 5 through 7 is known in the art. An input shaft 101 is connected to a steering shaft (not shown), and a pinion shaft 102 is connected to a rack (not shown) for turning vehicle steering wheels. A valve sleeve 103 is positioned on the outer periphery of the input shaft 101. The input shaft 101 is connected via a torsion bar (not shown) to the pinion shaft 102, so that the input shaft 101 and the pinion shaft 102 can relatively rotate by a defined small amount. A drive pin 104 is inserted into the outer periphery of the pinion shaft 102 along a radius thereof. When the input shaft 101 and the pinion shaft 102 are assembled, a pin hole 103a provided along the radius of the valve sleeve 103 receives the drive pin 104. The drive force for turning the vehicle steering wheels is transmitted through the steering shaft to the input shaft 101. When the input shaft 101 rotates relative to the valve sleeve 103, hydraulic liquid is forced from a hydraulic power source (not shown) through holes (not shown) in the valve sleeve 103 into a hydraulic cylinder (not shown). The piston of the hydraulic cylinder moves the rack, thereby rotating the pinion shaft 102 and the valve sleeve 103. A relative rotation angle is formed between the input shaft 101 and the pinion shaft 102 according to external forces such as the thrust of the rack. The relative rotation angle is small as described above. Hydraulic liquid is forced through the holes in the valve sleeve 103 when the relative rotation angle is present.
When the valve assembly is assembled, the drive pin 104 in the pinion shaft 102 is inserted into the pin hole 103a of the valve sleeve 103. Specifically, when the input shaft 101 is inserted into the pinion shaft 102, the drive pin 104 is set in the pin hole 103a. When the drive pin 104 engages the pin hole 103a of the valve sleeve 103, dimension L1 is obtained as shown in FIG. 6. To allow assembly the inner diameter D.sub.2 of the valve sleeve 103 is larger than the dimension L.sub.1. Engagement extent .delta. is thus limited. As a result, durability of the drive pin 104 is marginal. Wear on the drive pin 104 resulting from normal use causes hydraulic pressure reaction on an automotive steering wheel. To increase the durability and strength, the dimension of the drive pin 104 and associated components can be enlarged so that the area for receiving pressure is increased. However, this makes the valve assembly large-sized.